Fire resistant radiating coaxial cable

Abstract

A fire resistant radiating coaxial cable that employs a high-silica fiberglass yarn spacer is described. The yarn material has mass fraction of silica (SiO2) between 95.0% and 96.5%, a mass fraction of aluminum oxide (Al2O3) greater than 3%, and a mass fraction of calcium oxide (CaO) less than 0.5%. The yarn can be wound in a low-helix-angle helix around the center conductor such that less than half fills the annular space between it and the outer conductor. The cable is configured to maintain a relatively coaxial relation between a center conductor and an outer conductor under intense fire conditions.

What is claimed is: 
     
         1 . A fire resistant radiating coaxial cable apparatus comprising:
 a center conductor;   an outer conductor having a circumference with apertures, the outer conductor surrounding the center conductor; and   a high silica fiberglass yarn between the center conductor and the outer conductor, the fiberglass yarn having a mass fraction of silica (SiO 2 ) between 95.0% and 96.5%, a mass fraction of aluminum oxide (Al 2 O 3 ) greater than 3%, and a mass fraction of calcium oxide (CaO) less than 0.5%, the fiberglass yarn being configured to maintain a predetermined dielectric spacing between the center conductor and the outer conductor when exposed to heat at or above 1010° C.   
     
     
         2 . The apparatus of  claim 1  wherein the fiberglass yarn is wrapped in a helix around the center conductor. 
     
     
         3 . The apparatus of  claim 2  wherein the helix has an average helix angle of less than 60°. 
     
     
         4 . The apparatus of  claim 1  wherein the yarn fills less than half of a volume between the center conductor and the outer conductor. 
     
     
         5 . The apparatus of  claim 4  wherein the yarn fills less than a third of the volume between the center conductor and the outer conductor. 
     
     
         6 . The apparatus of  claim 1  wherein the yarn has two or more plies. 
     
     
         7 . The apparatus of  claim 1  wherein the yarn is a braided yarn. 
     
     
         8 . The apparatus of  claim 1  wherein the fiberglass yarn directly touches the center conductor or the outer conductor. 
     
     
         9 . The apparatus of  claim 1  wherein the high silica fiberglass yarn has a composition weight percentage of:
 (a) Na 2 O=0.0564%±0.0056% 
 (b) MgO=0.110%±0.011% 
 (c) Al 2 O 3 =3.55%±0.36% 
 (d) SiO 2 =96.0%±1.0% 
 (e) CaO=0.116%±0.012% 
 (f) Fe 2 O 3 =0.164%±0.016% 
 (g) ZrO 2 =0.0301±0.0030%. 
 
     
     
         10 . The apparatus of  claim 1  wherein the outer conductor is corrugated, the apertures having been produced by milling, at a constant radius, protuberant portions of corrugations along a length of the cable, the milling breaking through the outer conductor. 
     
     
         11 . The apparatus of  claim 1  wherein the outer conductor is a metal foil. 
     
     
         12 . The apparatus of  claim 1  wherein the outer conductor is a loose braid, wherein the apertures are between metal strands of the loose braid. 
     
     
         13 . The apparatus of  claim 1  further comprising:
 a ceramifiable silicone rubber inner jacket or a ceramic fiber wrap inner jacket surrounding the outer conductor. 
 
     
     
         14 . The apparatus of  claim 13  further comprising:
 a smooth outer jacket surrounding the inner jacket. 
 
     
     
         15 . The apparatus of  claim 14 , wherein the outer jacket includes an embossing or engraving aligned with the apertures. 
     
     
         16 . The apparatus of  claim 1  wherein the apertures were laser cut. 
     
     
         17 . A fire resistant coaxial cable apparatus comprising:
 a center conductor;   an outer conductor surrounding the center conductor; and   a high silica fiberglass yarn wrapped in a helix between the center conductor and the outer conductor, the fiberglass yarn having a mass fraction of silica (SiO 2 ) between 95.0% and 96.5%, a mass fraction of aluminum oxide (Al 2 O 3 ) greater than 3%, and a mass fraction of calcium oxide (CaO) less than 0.5%, the fiberglass yarn being configured to maintain a predetermined dielectric spacing between the center conductor and the outer conductor when exposed to heat at or above 1010° C.,   wherein the fiberglass yarn fills less than half of a volume between the center conductor and the outer conductor.   
     
     
         18 . The apparatus of  claim 17  wherein the outer conductor has corrugations with apertures, the apertures having been produced by milling, at a constant radius, protuberant portions of corrugations along a length of the cable, the milling breaking through the outer conductor. 
     
     
         19 . A method of manufacturing a fire resistant coaxial cable, the method comprising:
 wrapping a center conductor with a helix of high silica fiberglass yarn, the fiberglass yarn having a mass fraction of silica (SiO 2 ) between 95.0% and 96.5%, a mass fraction of aluminum oxide (Al 2 O 3 ) greater than 3%, and a mass fraction of calcium oxide (CaO) less than 0.5%; and   surrounding the fiberglass yarn and center conductor with an outer conductor, wherein the fiberglass yarn is configured to maintain a predetermined dielectric spacing between the center conductor and the outer conductor when exposed to heat at or above 1010° C.   
     
     
         20 . The method of  claim 19  wherein the outer conductor is corrugated, the method further comprising:
 milling, at a constant radius, apertures through protuberant portions of corrugations along a length of the cable, the milling breaking through the outer conductor.